1. Field of the Invention
The present invention relates to a plasma processing apparatus for carrying out plasma processing, such as film deposition, etching and ashing, on surfaces of insulated substrates such as semiconductor substrates and glass substrates.
2. Description of the Related Art
Liquid crystal display panels have recently been used widely as display units for word processors, personal computers, television sets and the like. A liquid crystal display panel is structured such that two electrode substrates, each of which is obtained by forming a plurality of thin films made of metal, semiconductor or the like on a transparent substrate made of glass or the like, and by subjecting the thin films to patterning by photo-lithography into desired shapes, are bonded to each other with their electrode-formed surfaces facing each other and with a predetermined space provided therebetween, and the space is filled with liquid crystals.
Processing, such as film deposition, etching and ashing, carried out in processing steps of forming a plurality of thin films made of metal, semiconductor, etc. in desired shapes on transparent substrates has conventionally been carried out in the processing chamber of a plasma processing apparatus as shown in FIG. 12.
Ref erring to FIG. 12, a substrate 7 is loaded from a vacuum or atmospheric system connected to a processing chamber 50 to the processing chamber 50 by a transfer robot (not shown). Generally, the arm of the transfer robot is held in a horizontal condition, and the substrate 7 is mounted thereon. When the substrate 7 is loaded into the processing chamber 50 by using the transfer robot, a space must be reserved between a susceptor 2 and the substrate 7 to allow the arm to be inserted into the space. For this purpose, independently of the susceptor 2, at least four vertically-movable lifting pins 1 are disposed in an area inside the periphery of the substrate 7. Furthermore, to center the substrate 7, a movable centering pin 3 may be disposed independently of the susceptor 2 and the lifting pins 1. By this centering pin 3, the substrate 7 is aligned with a shadow frame 5 used as an evaporation mask for plasma processing. The shadow frame 5 is used to surround and cover several millimeters of the periphery of the upper surface of the substrate 7, and can protect the edge and the backside of the substrate 7 against evaporation. The processing chamber 50, which is made of some metal pieces of aluminum, aluminum alloy or stainless steel, comprises an inner wall 100 which isolates the internal thereof from outside air on a shower plate 8, an inner wall 101 which encloses an inlet 103 to a pump f or drawing air in the processing chamber by suction, and an inner wall 102 (not shown) which is introduced into the processing chamber 50.
Before plasma processing, the susceptor 2 lifts the substrate 7 and the shadow frame 5 while moving upward. At this time, the centering pin 3 and the lifting pins 1 move independently to their retraction positions so that the surface of the susceptor 2 can make contact with the surface of the substrate 7.
After plasma processing, the susceptor 2 moves downward. At this time, the shadow frame 5 stops moving at the receiving portion 6a of the inner wall 6 of the processing chamber 50, thereby being away from the substrate 7.
Since high repeatability is required in production fields, it is indispensable to use a plasma processing apparatus capable of transferring substrates accurately by using the centering pin 3 and the like. Japanese Unexamined Patent Publication 6-340975(1994), for example, has disclosed a plasma processing apparatus having a configuration capable of accurately centering the substrates 7 at all times by performing centering by using the centering pin 3 being movable independently of the susceptor 2.
However, the conventional plasma processing apparatus has problems described below.
First, since the substrate 7 and the shadow frame 5 are lifted during processing, the susceptor 2 is required to be movable, thereby requiring a large-scale movement mechanism on the side of the susceptor 2 of the processing chamber 50. In particular, in the case that the processing chamber 50 is a single-substrate type, movement is repeated for each substrate 7. As a result, trouble is apt to occur at sealing members and ring portions at the boundary portions between the vacuum area thereof and the atmosphere.
Furthermore, the centering pin 3 can carry out centering when the substrate 7 is mispositioned slightly. However, if the substrate 7 is mispositioned significantly, the centering pin 3 will apply extra large force to the substrate 7. If this occurs during processing, such as film deposition, the substrate 7 is warped significantly, thereby making the processing impossible.
Furthermore, since the shadow frame 5 is just loosely mounted on the receiving portion 6a of the inner wall 6 of the processing chamber 50, a load is required to be applied thereto so that the shadow frame 5 functions as a mask for the substrate 7. Moreover, the horizontality of the processing chamber 50 is required to be high.
Besides, since the shadow frame 5 and the substrate 7 make contact with each other each time the processing is carried out, movement before and after processing cannot be performed at high speed in the case that the substrate 7 is formed of glass in particular.